The present invention relates to a new and improved construction of a headbox arrangement for forming multi-ply paper webs upon a moving water pervious wire or forming web member or the like.
Headbox apparatuses for the formation of multi-ply paper webs are known, for instance, from German Pat. No. 899,896 and U.S. Pat. No. 3,923,593, granted Dec. 2, 1975 and U.S. Pat. No. 4,141,788, granted Feb. 27, 1979. In all these constructions of headboxes there is disclosed a headbox design, wherein the common nozzle channel which leads to the outlet slice, is subdivided into subpassages for the flow of different stock suspensions. With the headbox construction disclosed in German Pat. No. 899,896 there is provided as such flow divider facility a rigid, but adjustable tongue-like element; with the headbox construction of U.S. Pat. No. 3,923,593 there are provided flexible lamellae or plates for dividing the nozzle channel. With the headbox construction of U.S. Pat. No. 4,141,788 there are utilized flexible sheets which, in fact, extend past the outlet slice, so that there is obtained a separation of the individual stock jets until such time as they are deposited upon a forming wire.
With the headbox construction of U.S. Pat. No. 4,141,788 the aforementioned advantage is however acquired at the expense, that the flexible lamellae or sheets tend to adjust themselves within the nozzle channel of the headbox in such a manner that at both sides or faces thereof there prevails the same liquid pressure. This leads to the result that also the flow velocities at the regions of the nozzle channel at both sides of the lamellae or sheets are the same. Consequently, there are only afforded limited possibilities during the fabrication of different types of paper.